Fan blade edge

ABSTRACT

The invention relates to the blades of a fan wheel. The invention particularly relates to a hollow profiled blade for a fan wheel. A hollow profiled blade according to the invention for a fan wheel is made from a planar semi-finished product and has a leading edge and a trailing edge as well as a compression side and a suction side. A hollow area is formed in the interior of the hollow profiled blade whereby the part of the planar semi-finished product forming the one side of the hollow profiled blade extends over the part of the planar semi-finished product forming the other side of the hollow profiled blade.

The invention relates to the blades of a fan wheel. The invention particularly relates to the edge of a hollow profiled blade for a fan wheel.

The purpose of fan wheels in radial or axial fans is to convey and/or compress gaseous media, particularly air. Several blades are arranged in a fan wheel whereby the flow channels are developed between the blades. Each blade has a compression and a suction side. The manufacture of blades from metallic materials in sheet form as hollow profiled blades for fan wheels is known from the state of the art. The advantage of such a design is the possibility it affords of manufacturing a blade from a semi-finished product whereby the manufacture has economic advantages. The hollow profile form also has advantages with regard to the weight of the blade, whereby the load on the drive motor is reduced. In addition, material is saved by using this design, whereby costs can be reduced.

For example, the unexamined German application DE 10 2011 013 841 A1 discloses such a blade with a hollow profile made from a metallic material. Each hollow profiled blade is made from a semi-finished product whereby the blades have a cross-section of a load-bearing type. In particular the blade has a leading edge and a trailing edge whereby the leading edge is formed from the curved semi-finished product. The two ends of the semi-finished product meet such they lie flat on each other at the trailing edge. In doing so, this design takes account of the knowledge that a hollow profile blade has an ideal aerodynamic shape if its trailing edge is as thin as possible. In other words, for an aerodynamically ideal shape of a hollow profile blade it is necessary to have a trailing edge which has a wall thickness which is as thin as possible. In the example in the disclosure the wall thickness of the trailing edge is approximately twice the wall thickness of the semi-finished product which is used. Both ends of the semi-finished product can be joined to each other with known methods such as welding or hard soldering.

The blade profile of the disclosure also has a continuous progression of the surface contour. According to the opinion known in the state of the art, protrusions, ledges or similar in the blade geometry have a deleterious effect on the flow behavior.

A progression which is aerodynamically favorable occurs if the medium which is flowing moves if at all possible along the adjacent surface of the blades in such a manner that its velocity vectors are aligned as parallel as possible to the blade surface. Flow separations, turbulence or similar are normally undesirable as they cause losses in the flow. These flow situations which deviate from a beneficial flow progression reduce efficiency, impair the acoustic performance and can lead to unstable characteristic curves.

The problem of the invention is to indicate a hollow profiled blade for a fan wheel which optimizes the efficiency and acoustic performance of known hollow profiled blades. It is also the problem of the invention to indicate a fan wheel for a radial fan which exhibits improved efficiency and an improved acoustic performance compared with known fan wheels.

According to the invention, this problem is solved by a hollow profiled blade with the attributes of the independent claim 1. Advantageous developments of the hollow profiled blade result from sub-claims 2 to 22. The problem is further solved by a fan wheel according to claim 23 and claim 24.

A hollow profiled blade for a fan wheel according to the invention is manufactured from at least one first planar semi-finished product and has a leading edge and a trailing edge as well as a compression side and a suction side whereby the compression side has a first part of the first planar semi-finished product and the suction side has a second part of the first planar semi-finished product. Inside the hollow profiled blade is a hollow area in which the hollow profiled blade has a wall thickness in an area arranged in front of the trailing edge and immediately adjacent to the trailing edge which is less than twice the wall thickness of the first planar semi-finished product. This design achieves a blade with a trailing edge at the end with a very thin geometry whereby the hollow profiled blade is aerodynamically optimized. In addition, in the area of the trailing edge of the hollow profiled blade the first part of the first planar semi-finished product is bent through approximately 180° and passed inwards into the hollow area of the hollow profiled blade. The first part of the first planar semi-finished product which is passed inwards into the hollow area of the hollow profiled blade has the effect of reinforcing the hollow profiled blade whereby the deformations which are possible precisely in the area of the trailing edge of the blade during the operation of the blade are minimized. Alternatively, the second part of the first planar semi-finished product can be bent through approximately 180° and passed inwards into the hollow area of the hollow profiled blade, whereby the effect is the same.

In a preferred embodiment, in the area which is in front of the trailing edge and directly adjacent to the trailing edge, the hollow profiled blade has a wall thickness which corresponds essentially to the single wall thickness of the first planar semi-finished product.

As such, in one embodiment, the first part of the first planar semi-finished product can extend over and beyond the second part of the planar semi-finished product in the area which is in front of the trailing edge and directly adjacent to the trailing edge. For example, in a first embodiment the compression side of the hollow profiled blade can be formed from the first part of the first planar semi-finished product of the hollow profiled blade, while the suction side is formed from the second part of the first planar semi-finished product of the hollow profiled blade whereby the first part of the first planar semi-finished product extends over and beyond the second part of the planar semi-finished product in the area of the trailing edge of the blade. In an alternative embodiment the second part of the first planar semi-finished product can extend over and beyond the first part of the planar semi-finished product in the area of the trailing edge of the blade.

The planar semi-finished product normally consists of a sheet, for example of a metallic material. The sheet can be bent, for example, on a press brake.

In an advantageous embodiment the first part of the first planar semi-finished product of the hollow profiled blade is connected tightly and flush with the second part of the first planar semi-finished product. This connection can, for example, consist of a weld seam or also of individual spot welds. It is advantageous if the connection point lies in an area which is close to the trailing edge of the blade and positioned at a distance from the leading edge of the hollow profiled blade.

In a further particularly advantageous embodiment, the position of the bend of the first part of the first planar semi-finished product on the second part of the first planar semi-finished product forms an abrupt difference in thickness in the profile of the hollow profiled blade. The invention recognizes that contrary to the state of the art which stipulates a constant contour progression for a parallel, low loss flow over a blade, it can be possible to diverge from this under certain circumstances. If certain geometric ratios are maintained a largely parallel flow over the blade can be achieved in spite of an irregular progression of the blade.

In a further preferred embodiment, the first part of the first planar semi-finished product of the hollow profiled blade is welded to the second part of the first planar semi-finished product by a fillet weld. Surprisingly, the weld seam has only a small effect of the flow of the medium. A small area of turbulence forms in the flow in this area which, from the point of view of the flowing medium, almost equalizes the abrupt change in thickness of the hollow profile blade at this point and therefore encourages a parallel flow. Other forms of weld seams or alternatively spot welding are also possible but encourage the formation of a parallel flow at this point to a less optimal degree.

It has been shown to be advantageous if the length by which the second part of the first planar semi-finished product of the hollow profile blade extends over the position of the bend of the first part of the first planar semi-finished product is precisely so long that it is up to 100 times longer than the magnitude of the abrupt change in thickness. In other words it is advantageous if the ratio of the magnitude of the abrupt change in thickness to the length by which the second part of the first planar semi-finished product extends over the position of the bend of the first part of the first planar semi-finished product lies in the range from 1:1 to 1:100. In this case it has been shown to be particularly advantageous if this ratio lies in the range from 1:2 to 1:20. In such an order of magnitude the flow turbulence which forms at the abrupt change of thickness is particularly suited to minimize the aerodynamic effects of the abrupt change in thickness.

In an advantageous embodiment a stiffener profile is arranged in the interior of the hollow profiled blade. Deformations appear when the blades are operating, for example through the difference in pressure of the flow medium between the compression and the suction sides and as a result of centrifugal forces; these deformations usually occur in the elastic range of the material. As a result of these deformations the blade profile can change and the efficiency can be impaired thereby. In addition, a deformation of this nature can also influence noise emission. The stiffener profile reduces this potential deformation and therefore optimizes efficiency and noise emission during operations. The resultant mechanical tensions and deformations also limit the permissible rotational speed range.

In a further advantageous embodiment, the stiffener profile is formed from the reverse bent part of the first part of the first planar semi-finished product. This embodiment can be manufactured particularly easily whereby the advantage is particularly great if the stiffener profile can be made by bending.

It has also proved to be advantageous if, in the interior of the hollow profiled blade, a part of the first planar semi-finished product lies flat on one side of the hollow profiled blade in the region of the trailing edge. In this form, the area of the trailing edge includes not only the part lying directly on the trailing edge of the blade but also an area starting from about the central point between the leading edge and the trailing edge through to the trailing edge itself.

In an advantageous embodiment the part of the first planar semi-finished product in the interior of the hollow profiled blade lies flat on the suction side of the hollow profiled blade whereby the area of the trailing edge is defined as described above. This design can be manufactured particularly easily and leads to a hollow profiled blade which is optimized from the point of view of torsional stiffness. This development leads to the fact that in the corresponding region the hollow profiled blade exhibits a wall thickness which is three times that of the planar semi-finished product used for the manufacture of the blade, while the region of the trailing edge which extends beyond the reverse bent part of the first part of the first planar semi-finished product consists of only one layer of the first planar semi-finished product and therefore has a wall thickness of only one layer of the first planar semi-finished product which is used.

In a further advantageous embodiment the hollow profiled blade is manufactured from precisely one first planar semi-finished product whereby a particularly economic manufacturing process is possible.

In an alternative embodiment a second planar semi-finished product is arranged in the area which is in front of the trailing edge and directly adjacent to the trailing edge. In this embodiment this second planar semi-finished product extends over the first planar semi-finished product in the direction of the trailing edge of the hollow profiled blade. The wall thickness of the second planar semi-finished product is less than twice the wall thickness of the first planar semi-finished product. Thus also in this embodiment in the area which is in front of the trailing edge and immediately adjacent to the trailing edge a wall thickness of the hollow profiled blade is created which is less than twice the wall thickness of the first planar semi-finished product. In particular the wall thickness of the hollow profiled blade in the area which is in front of the trailing edge and directly adjacent to the trailing edge is equal to a single wall thickness of the second planar semi-finished product. This second planar semi-finished product can, for example, consist of a sheet of a metallic material like the first planar semi-finished product. Thus also in this alternative design a blade with a trailing edge at the end is achieved with a very thin geometry whereby the hollow profiled blade is aerodynamically optimized.

In an advantageous embodiment the second planar semi-finished product extends inwards into the interior of the hollow profiled blade. In this way the second planar semi-finished product can be fastened particularly easily and securely to the hollow profiled blade. In order to achieve this, in a further advantageous embodiment the second planar semi-finished product is connected tightly and flush with the first part of the first planar semi-finished product of the hollow profiled blade and/or with the second part of the first planar semi-finished product. It has proved to be advantageous if this tight and flush connection is achieved by welding, particularly by means of a fillet weld.

In the alternative embodiment it is also advantageous if a stiffener profile is arranged in the interior of the hollow profiled blade. It is particularly advantageous if the stiffener profile is formed from the second of the planar semi-finished products.

In an advantageous embodiment the stiffener profile is made by bending the second planar semi-finished product.

A fan wheel according to the invention for a radial fan has a top plate and a base plate and is characterized in that it has several hollow profiled blades between the top plate and the base plate. In this wheel the hollow profiled blades correspond to one of the embodiments described above.

In an advantageous embodiment of the fan wheel according to the invention the hollow profiled blades have lugs on one of their upper and/or lower narrow side, while the top plate and/or the base plate have slots into which the lugs can be inserted to hold the hollow profiled blades into position between the top plate and the base plate whereby a particularly simple assembly of the hollow profiled blades in the fan wheel is achieved.

Further advantages, peculiarities and useful developments of the invention arise from the sub-claims and the following representation of preferred embodiments by reference to the Figures.

The various Figures show:

FIG. 1 A hollow profiled blade according to the state of the art in a three dimensional presentation

FIG. 2 A diagram of the flow pattern at the trailing edge of a hollow profiled blade according to the state of the art

FIG. 3 A three dimensional presentation of a hollow profiled blade according to the invention

FIG. 4 A three dimensional presentation of an alternative embodiment of a hollow profiled blade according to the invention

FIG. 5 A three dimensional presentation of a further alternative embodiment of a hollow profiled blade according to the invention

FIG. 6 A cross sectional view of the alternative embodiment in FIG. 5

FIG. 7 A three dimensional presentation of further embodiment of a hollow profiled blade according to the invention with an internal stiffener profile.

FIG. 8 A cross sectional view of the embodiment of the hollow profiled blade according to the invention with an internal stiffener profile in FIG. 4.

FIG. 9 A detailed presentation of the trailing edge of a hollow profiled blade according to the invention in a cross sectional view

FIG. 10 A diagram of the flow pattern of a hollow profiled blade according to the invention

FIG. 11 A detailed presentation of a flow pattern diagram at the trailing edge of a hollow profiled blade according to the invention

FIG. 12 A three dimensional presentation of a fan wheel according to the invention

FIG. 1 shows a hollow profiled blade 100 according to the state of the art in a three dimensional presentation. The hollow profiled blade 100 is manufactured from a first sheet in the form of a planar semi-finished product 105 and has a compression side 130, a suction side 140, a leading edge 110 and a trailing edge 120. A hollow interior 101 is formed between the compression side 130 and the suction side 140. The sheet 105 is bent in such a manner that the leading edge 110 has a thickness which is greater than twice the wall thickness of the sheet 105. In contrast, at the trailing edge 120 the ends of the sheet lie on top of each other in such a manner that the trailing edge 120 has a thickness which is of the magnitude of twice the wall thickness of the sheet used 105.

FIG. 2 shows a diagram of the flow pattern at the trailing edge 120 of a hollow profiled blade 100 according to the state of the art. The hollow profiled blade 100 is made from sheet. The sheet 105 forming the compression side 130 and the suction side 140 meet on top of one another at the trailing edge. A hollow area 101 is formed in the area in front of the trailing edge. In addition, flow lines 150 of a medium flowing round the hollow profiled blade, for example air, can also be seen. The medium flows round the hollow profiled blade 100 in a manner which is very largely parallel. In addition, turbulence 151, which is created by the abrupt edge in the form of the sheets lying on top of each other 105 with a thickness of approximately twice that of the sheet thickness can be seen at the trailing edge 120 of the hollow profiled blade 100. This turbulence leads to a deterioration in the efficiency of the hollow profiled blade 100. In addition, undesirable acoustic effects can occur as a result of the turbulence.

A tree dimensional representation of a hollow profiled blade according to the invention 100 can be seen in FIG. 3. The hollow profiled blade 100 is manufactured from a sheet as the first planar semi-finished product 105 and has a compression side 130, a suction side 140, a leading edge 110 and a trailing edge 120. A hollow interior 101 is formed between the compression side 130 and the suction side 140. The sheet 105 is bent in such a manner that the leading edge 110 has a thickness which is greater than twice the wall thickness of the sheet 105. The ends of the sheet lie on top of each other in a region 126 which is arranged in front of the trailing edge 120 and directly adjacent to the trailing edge 120. The compression side 130 of the hollow profiled blade 100 has a first part 105 d of the first planar semi-finished product 105 and the suction side 140 of the hollow profiled blade 100 has a second part 105 s of the first planar semi-finished product. In this, the second part 105 s of the first planar semi-finished product 105 extends over the first part 105 d of the first planar semi-finished product 105 in such a manner that the trailing edge 120 itself has a thickness which is the thickness of a single sheet. In this, the suction side 130 has an abrupt increase in thickness 141 at the position at which the first part 105 d of the first planar semi-finished product meets the second part 105 s of the first planar semi-finished product.

FIG. 4 shows the three dimensional presentation of an alternative embodiment of a hollow profiled blade according to the invention. Unlike the embodiment shown in FIG. 3, the first part 105 d of the first planar semi-finished product 105 extends over the second part 105 s of the first planar semi-finished product 105 in the region 126. Also in this embodiment the trailing edge 120 itself has a thickness of one sheet. As part of this, the compression side 140 has an abrupt increase in thickness 141 at the position at which the second part 105 s of the first planar semi-finished product 105 meets the first part 105 d of the first planar semi-finished product 105.

FIG. 5 is the three dimensional presentation of a further alternative embodiment of a hollow profiled blade according to the invention 100. In this embodiment the compression side 130 has a first part 105 d of the first planar semi-finished product 104, while the suction side 140 has a second part 105 s of the first planar semi-finished product 105. In the area 126 arranged in front of the trailing edge 120 and directly adjacent to the trailing edge 120 there is a second planar semi-finished product 107 which projects into the interior 101 of the hollow profiled blade 100 and which also extends both over the first part 105 d and the second part 104 s of the first planar semi-finished product 105 in the direction of the trailing edge 120. The wall thickness of the second planar semi-finished product 107 is less than twice the wall thickness of the first planar semi-finished product 105. For example, the wall thickness of the second planar semi-finished product 107 has essentially the same wall thickness as the first planar semi-finished product 105. In this arrangement a wall thickness of the hollow profiled blade 100 is created in the area 126 also in this embodiment which is smaller than twice the wall thickness of the first planar semi-finished product 105. Thus also by this alternative design a hollow profiled blade 105 with a trailing edge at the end 120 is achieved with a very thin geometry whereby the hollow profiled blade 100 is aerodynamically optimized.

FIG. 6 is a cross sectional view of the alternative embodiment in FIG. 5. The second semi-finished product 107 is introduced into the interior 101 of the hollow profiled blade 100 between the first part 105 d and the second part 105 s of the first planar semi-finished product 105 and is welded both to the first part 105 d and the second part 105 s of the first planar semi-finished product 105.

FIG. 7 shows in a three dimensional presentation a further embodiment of a hollow profiled blade according to the invention 100 with an internal stiffener profile 125. The first part 105 d of the first planar semi-finished product 105 is bent through approximately 180° at the place where it meets the second part 105 s of the first planar semi-finished product 105 in front of the trailing edge 120 and directly adjacent to the trailing edge 120 in the area 126 and is introduced and supported back into the interior 101 of the hollow profiled blade 100 at the internal side of the second part 105 s of the first planar semi-finished product. This first part 105 d of the first planar semi-finished product 105 is bent at its end and in this way forms a stiffener profile 125. By returning the first part 105 d of the first semi-finished product 105, the hollow profiled blade has a thickness which is three times the thickness of the sheet in an area 123 from the point where the sheet is bent 122 to the end of the sheet which is turned inwards 105. In this way the hollow profiled blade 100 is strengthened in this area and is therefore better able to resist the deformation forces which occur during operation. The stiffener profile 125 makes a further contribution to stabilizing the hollow profiled blade 100.

FIG. 8 is a cross sectional view of the embodiment of the hollow profiled blade according to the invention 100 shown in FIG. 4 and with an internal stiffener profile. In this presentation the area 123 in which the first part 105 d of the first planar semi-finished product 105 is introduced back into the interior 101 and lies on top of the second part 105 s of the first planar semi-finished product can be seen more clearly. The stiffener profile 125 can be made as shown in FIG. 7. However, other geometries capable of resisting a bending or torsional moment are also conceivable.

In FIG. 9 the trailing edge 120 of a hollow profiled blade according to the invention 100 is shown in an enlarged form. The first part 105 d of the first planar semi-finished product 105 is bent through approximately 180° at the position of the bend 122 and introduced back into the interior 101 of the hollow profiled blade 100 on top of the second part 105 s of the first planar semi-finished product 105 whereby the second part 105 s of the first planar semi-finished product 105 is extended over the position of the bend 122 in the direction of the trailing edge 120. The parts 105 d and 105 s of the first planar semi-finished product 105 are welded together tightly and flush with each other with a fillet weld 121 at the position of the bend 122.

FIG. 10 shows a diagram of the flow pattern of a hollow profiled blade according to the invention 100. When the blade rotates in the x direction the parallel flow pattern shown is formed.

In FIG. 11 the flow pattern which forms at the trailing edge 120 of a hollow profiled blade according to the invention 100 is shown in an enlarged diagram. A small area of turbulence 152 forms in the area of the fillet weld 121 which, from the point of view of the flowing medium, almost equalizes the abrupt change in thickness 141 of the hollow profile blade 100 at this point and therefore encourages a parallel, low-loss flow.

FIG. 12 is the three dimensional presentation of a fan wheel according to the invention 200. The fan wheel 200 has a top plate 210 and a base plate 220. Hollow profiled blades 100 are arranged between the base plate 220 and the top plate 210. The hollow profiled blades 100 can be installed in the fan wheel 200 by means of lugs 106 which fit into slots 211 in the top plate 210 and further lugs which fit into slots in the base plate (not shown in the Figure).

The embodiments shown here only represent examples of this invention and therefore must not be understood as restrictive. Alternative embodiments considered by a person skilled in the art are included equally in the extent of protection of this invention.

LIST OF REFERENCE NUMBERS

-   -   100 Hollow profiled blade     -   101 Hollow area, interior     -   105 Planar semi-finished product, sheet     -   105 d First part of the first planar semi-finished product         arranged on the compression side     -   105 s Second part of the first planar semi-finished product         arranged on the suction side     -   106 Lug     -   107 Second planar semi-finished product, sheet     -   110 Leading edge     -   120 Trailing edge     -   121 Fillet weld     -   122 Position of the bend/bend position     -   123 Area of the returned planar semi-finished product     -   125 Stiffener profile     -   127 Area, region     -   130 Compression side     -   140 Suction side     -   141 Abrupt change of thickness     -   150 Flow line     -   151 Turbulence     -   152 Flow turbulence     -   200 Fan wheel     -   210 Top plate     -   211 Slot     -   220 Base plate     -   x Direction of rotation 

1. A hollow profiled blade for a fan wheel whereby the hollow profiled blade is manufactured from at least a first planar semi-finished product and has a leading edge and a trailing edge as well as a compression side and a suction side and whereby a hollow area is formed in the interior of the hollow profiled blade whereby the compression side has a first part of the first planar semi-finished product and the suction side has a second part of the first planar semi-finished product, characterized in that the hollow profiled blade has a wall thickness which is less than twice the wall thickness of the first planar semi-finished product in an area which is arranged in front of the trailing edge and directly adjacent to the trailing edge.
 2. A hollow profiled blade according to claim 1 characterized in that the hollow profiled blade has a wall thickness in the area which essentially corresponds to the wall thickness of the first planar semi-finished product.
 3. A hollow profiled blade according to claim 1 characterized in that the first part of the first planar semi-finished product extends beyond the second part of the planar semi-finished product in the area.
 4. A hollow profiled blade according to claim 1 characterized in that the second part of the first planar semi-finished product extends over the first part of the planar semi-finished product in the area.
 5. A hollow profiled blade according to claim 1 characterized in that the first part of the planar semi-finished product of the hollow profiled blade is connected tightly and flush with the second part of the first planar semi-finished product.
 6. A hollow profiled blade according to claim 4 characterized in that the position of the bend of the first part of the first planar semi-finished product forms an abrupt change in thickness in the profile of the hollow profiled blade on the second part of the first planar semi-finished product.
 7. A hollow profiled blade according to claim 6 characterized in that the first part of the planar semi-finished product of the hollow profiled blade is welded tightly and flush to the second part of the first planar semi-finished product by a fillet weld.
 8. A hollow profiled blade according to claim 6 characterized in that the ratio of the magnitude of the abrupt change in thickness to the length by which the second part of the first planar semi-finished product of the hollow profiled blade extends over the position of the bend of the first part of the first planar semi-finished product lies in the range from 1:1 to 1:100.
 9. A hollow profiled blade according to claim 6 characterized in that the ratio of the magnitude of the abrupt change in thickness to the length by which the second part of the first planar semi-finished product of the hollow profiled blade extends over the position of the bend of the first part of the first planar semi-finished product lies in the range from 1:2 to 1:20.
 10. A hollow profiled blade according to claim 1 characterized in that, a stiffener profile is arranged in the interior of the hollow profiled blade.
 11. A hollow profiled blade according to claim 10 characterized in that, the stiffener profile is formed from the bent portion of the first part of the first planar semi-finished product.
 12. A hollow profiled blade according to claim 10 characterized in that the stiffener profile can be manufactured by bending.
 13. A hollow profiled blade according to claim 1 characterized in that a part of the first planar semi-finished product lies flat on one side of the hollow profiled blade in the interior of the hollow profiled blade in the area of the trailing edge.
 14. A hollow profiled blade according to claim 13 characterized in that the overlying part of the first planar semi-finished product in the area of the trailing edge lies flat on the suction side of the hollow profiled blade in the interior of the hollow profiled blade.
 15. A hollow profiled blade according to claim 1 characterized in that the hollow profiled blade is made from precisely a first planar semi-finished product,
 16. A hollow profiled blade according to claim 1 characterized in that, in the area a second planar semi-finished product is arranged whereby this second planar semi-finished product extends over the first planar semi-finished product in the direction of the trailing edge of the hollow profiled blade and whereby the wall thickness of the second planar semi-finished product is less than twice the wall thickness of the first planar semi-finished product.
 17. A hollow profiled blade according to claim 16 characterized in that, the second planar semi-finished product extends into the interior of the hollow profiled blade.
 18. A hollow profiled blade according to claim 16 characterized in that the first part of the first planar semi-finished product of the hollow profiled blade and/or the second part of the first planar semi-finished product is connected tightly and flush with the second planar semi-finished product.
 19. A hollow profiled blade according to claim 18 characterized in that, the first part of the first planar semi-finished product of the hollow profiled blade and/or the second part of the first planar semi-finished product is welded to the second planar semi-finished product by a fillet weld.
 20. A hollow profiled blade according to claim 16 characterized in that a stiffener profile is arranged in the interior of the hollow profiled blade.
 21. A hollow profiled blade according to claim 20 characterized in that, the stiffener profile is formed from the second of the planar semi-finished products.
 22. A hollow profiled blade according to claim 20 characterized in that the stiffener profile can be manufactured by bending.
 23. A fan wheel for a radial fan with a top plate and a base plate, characterized in that, the fan wheel has several hollow profiled blades between the top plate and the base plate.
 24. A fan wheel according to claim 23, characterized in that, the hollow profiled blades have lugs in its upper and/or lower narrow side, while the top plate and/or the base plate have slots into which the lugs can be inserted to secure the hollow profiled blades between the top plate and the base plate. 